Hydrophobic polymers are often used in photographic elements as overcoats or binders. Such polymers are water resistant and have a reduced tendency to stick to hydrophilic surfaces such as photographic emulsion, under conditions of high temperature and relative humidity. The latter phenomenon is referred to as ferrotyping in the photographic arts. Hydrophobic polymers having a glass transition temperature (Tg) above about 70.degree. C. are resistant to ferrotyping. Such polymers are often coated from organic solvent-based solutions. Continuous films are formed simply by evaporation of the solvent.
Polymer particles of aqueous latex compositions used for making coatings on photographic film generally have a Tg less than about 70.degree. C. in order to achieve coalescence of the polymer particles to a continuous film. Under temperature and residence time conditions generally used in making coatings on photographic film bases and layers, it is normally not possible to fully coalesce a water-borne latex polymer to a continuous film if the Tg exceeds about 70.degree. C., unless volatile organic coalescing aids are utilized. This represents a severe limitation since such materials must be removed from the final film.
However, because of economic and environmental considerations, there is a need to replace organic solvent-based coating systems with water-based coating systems. In order to fill this need, it is necessary to form continuous films from latex polymers which are resistant to ferrotyping.
Core-shell latex polymer particles are disclosed in Kobunshi Ronbunshu, Eng. Ed., Vol. 5, No. 11, 1976, page 894. However, these polymers do not form coalesced continuous layers.